Process for evaluating corrosion resistance of coating

ABSTRACT

The present invention is directed to a process for corrosion resistance evaluation of coated metals substrates, such as autobodies. An anode and cathode coated with protective coating being tested are exposed to an electrolyte in a chamber of a corrosion resistance evaluator. These coatings are provided with predetermined and standardized defects, such as micro-holes to accelerate the corrosion of the underlying metal substrate in a predictable and repeatable manner. The coated cathode/anode pair is subject to a start-up period followed by series preset DC voltages for preset durations that are interspaced with recovery periods. The impedance data collected are then used to arrive at the corrosion performance resistance of the coating applied over the cathode/anode pair. The foregoing evaluator substantially reduces the time required to test corrosion from several days (40 plus days) to few days (about two days).

FIELD OF INVENTION

This application claims priority from U.S. Provisional Ser. No.61/204159 filed on Jan. 2, 2009 and U.S. Provisional Ser. No. 61/289484filed Dec. 23, 2009, both of which are hereby incorporated herein byreference.

The present invention is directed to a corrosion resistance evaluatorsuitable for evaluating the corrosion resistance of multi-coated andsingle coated metal substrates and more particularly directed to acorrosion resistance evaluator and to a process used therein forevaluating the corrosion resistance of multi-coated and single coatedmetal substrates at an accelerated rate.

BACKGROUND OF INVENTION

Currently, no short term (less than 2 days) test method exists toevaluate the long-term corrosion protection afforded by a protectivecoating from a coating composition, such as automotive OEM or automotiverefinish coating compositions, applied over a metal substrate, such asautomotive body. The current standard test methods rely primarily onenvironmental chamber exposure, followed by visual and mechanicaltesting of the metal with its protective coating. This kind of testingis long (up to 40 days or more exposure time), subjective, highlydependent on the exposure geometry, and on the person doing theevaluation. Consequently, these methods are not very reproducible. Thecorrosion resistance data is qualitative, and therefore the relativeperformance of an acceptable coating cannot be easily determined. Anynew test method must correlate well with the traditional, the accepted,standard environmental chamber test methods, must be reproducible, andmust supply a qualitative and quantitative ranking of the unknowndirect-to-metal (DTM) corrosion resistant coating.

The experimental corrosion test methods have been reported for reducingthe test duration. These methods primarily utilize electrochemicalimpedance spectroscopy (EIS) or AC impedance technology. Since these ACimpedance based methods typically only offer a more sensitive tool fordetecting corrosion at an early stage of exposure time, the corrosionprocess itself is not accelerated by these methods. Therefore, thesemethods still require relatively long exposure times before themeaningful data can be obtained. The length of time needed to getmeaningful corrosion data approaches that of the standard methods. Moreimportantly, the corrosion resistance data obtained by these methods,particularly during the initial exposure time, are primarily dictated bythe intrinsic defects of the coatings. These intrinsic defects generallyproduced during the preparation of coated samples are not necessarilyrelated to the actual performance of the coatings. Misleadinginformation could be obtained if the data are not analyzed correctly.Consequently, the standard convention methods are still favored.Therefore, a need still exists for a device and a process that not onlyaccelerates the corrosion of protectively coated metal substrates butalso mimics the corrosion typically seen in working environments, suchas those experienced by bodies of automobiles during use.

STATEMENT OF INVENTION

The present invention is directed to a process for evaluating corrosionresistance of an anode coating applied over a surface of an anode andcorrosion resistance of a cathode coating applied over a surface of acathode comprising:

(i) sealably positioning said anode in an anode holder located on achamber of a corrosion resistance evaluator, said chamber containing anelectrolyte therein such that a portion of said anode coating is exposedto said electrolyte, said portion of said anode coating having an anodedefect thereon;

(ii) sealably positioning said cathode in a cathode holder located onsaid chamber such that a portion of said cathode coating is exposed tosaid electrolyte, said portion of said cathode coating having a cathodedefect thereon;

(iii) directing a computer of said evaluator through computer readableprogram code means residing on a usable storage medium located in saidcomputer and configured to cause said computer to perform followingsteps comprising:

-   -   a) subjecting said portions of said anode coating and said        cathode coating to a start-up period;    -   b) directing an impedance measurement device in communication        with said computer and is connected to said cathode and said        anode to measure n1 set of impedances A during said start-up        period at preset intervals, wherein each said set of ac        impedances A are measured at preset frequencies ranging from        100000 to 10⁻⁶ Hz of AC power at desired AC voltages with an        amplitude ranging from 10 to 50 mV supplied by an alternating        current variable power generator in communication with said        computer, said alternating current variable power generator        having AC output leads that connect to said cathode and anode;    -   c) determining start-up solution resistances (^(Sta)R_(sol.n1))        by selecting a real part of said impedance A at a start-up        solution frequency selected from 500 to 100000 Hz from each said        set of said impedances A;    -   d) determining start-up resistances (^(Sta)R_(Sta.n1)) by        selecting a real part of impedance A at a start-up frequency        selected from 10⁻¹ to 10⁻⁶ Hz from each said set of said        impedances A;    -   e) directing a direct current variable power generator to apply        n2 preset DC voltages in a stepwise manner for n2 preset        durations, wherein said direct current variable power generator        is in communication with said computer and is connected to said        cathode and said anode; and wherein said direct current        measurement device in communication with said computer and        connected to said cathode and said anode is used to measure said        preset DC voltages;    -   f) directing said impedance measurement device to measure a set        of impedances B at the end of each of said preset duration at        said preset frequencies of AC power with said amplitude supplied        by said alternating current variable power generator to produce        n2 said sets of said impedances B;    -   g) determining stepped-up solution resistances        (^(Stp)R_(sol.n2)) by selecting a real part of said impedance B        at stepped-up solution frequency selected from 500 to 100000 Hz        from each said set of said impedances B;    -   h) determining stepped-up resistances (^(Stp)R_(stp.n2)) by        selecting a real part of impedance B at a stepped-up frequency        selected from 10⁻¹ to 10⁻⁶ Hz from each said set of said        impedances B;    -   i) subjecting said portions of said anode coating and said        cathode coating to n3 preset recovery periods in between each of        said preset durations;    -   j) directing said impedance measurement device to measure a set        of impedances C at the end of each of said preset recovery        periods at said preset frequencies of AC power with said        amplitude supplied by said alternating current variable power        generator to produce n3 said sets of said impedances C;    -   k) determining recovery solution resistances (^(Rec)R_(sol.n3))        by selecting a real part of impedance C at a recovery frequency        selected from 500 to 100000 Hz from each said set of said        impedances C;    -   l) determining recovery resistances (^(Rec)R_(Rec.n3)) by        selecting a real part of impedance C at recovery frequency        selected from 10⁻¹ to 10⁻⁶ Hz from each said set of said        impedances C;    -   m) calculating corrosion performance resistance (R_(perf)) of        said anode and said cathode pair by using the following        equation:

R _(perf)=[Σ^(Sta) f _(n1)(^(Sta) R _(Sta.n1)−^(Sta) R_(Sol.n1))]/n1+[Σ^(Stp) R _(Stp.n2)−^(Stp) R _(Sol.n2))]/n2+[Σ^(Rec) f_(n3)(^(Rec) R _(Rec.n3)−^(Rec) R _(Sol.n3))]/n3, wherein n1, n2, n3 andn3 range from 1 to 100; and ^(Sta) f _(n1), ^(Stp) f _(n2), and ^(Rec) f_(n3) range from 0.0000001 to 1; and

-   -   n) causing computer 40 to direct a computer monitor 52 to:        -   (n1) display the corrosion performance resistance            (R_(perf)),        -   (n2) direct a printer 54 to print the corrosion performance            resistance (R_(perf)),        -   (n3) transfer the corrosion performance resistance            (R_(perf)) to a remote computer 56 or a remote database, or        -   (n4) a combination thereof.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 broadly illustrates the process of anodic metal dissolution thatoccurs at anode.

FIG. 2 broadly illustrates the process of delamination that occurs atcathode.

FIG. 3 illustrates a longitudinal cross-sectional view of one embodimentof the corrosion resistance evaluator of the present invention.

FIG. 4A, 4B, 4C and 4D represent a flowchart of means for configuringcomputer readable program code means used in the device of the presentinvention illustrated in FIG. 3.

FIG. 5 illustrates one of the typical protocols used in the process ofthe present invention.

FIGS. 6 and 7 illustrate the deliberately created artificial defects onanode and cathode coatings for exposing the underlying surface of metalanodes and cathodes.

FIG. 8 illustrates a plan view of yet another embodiment of the presentinvention that provides for multiple chambers.

FIG. 9 illustrates a cross-sectional view of the embodiment of FIG. 8taken along the cross-section 9-9, illustrating the expeditious meansfor permitting escape of gases generated during the corrosion testingprocess.

FIG. 10 illustrates the Nyquist plot of AC impedance data obtained onE-coat H during start up period.

FIG. 11 illustrates the expanded left part of the Nyquist plot of acimpedance data obtained on E-coat H during start up period.

FIG. 12 illustrates the expanded right part of the Nyquist plot of acimpedance data obtained on E-coat H during start up period.

FIG. 13 illustrates the correlation and comparison of the resultsobtained by using the corrosion evaluation process of current inventionagainst those obtained by using a well known conventional cycliccorrosion evaluation test.

DETAILED DESCRIPTION OF PREFERRED THE EMBODIMENT

The evaluation of corrosion resistance of single layer or multilayerprotective coatings, such as those resulting from an automotive OEMpaint, an automotive refinish paint, a marine paint, an aircraft paint,an architectural paint, an industrial paint, a rubberized coating, apolytetrafluoroethylene coating, or a zinc-rich primer, typicallyapplied over metal substrates, such as steel, aluminum and copper, isvery important for determining the working life of a product, such as anautomobile, a ship or a crane.

When a metal substrate, such as an automobile body, is exposed toatmosphere, its surface is covered by a thin film of water produced bythe condensation of moisture in air, although it may not be visible dueto the extremely low thickness of the film. Many micro electrochemicalcorrosion cells can develop on the surface of metal substrate underneaththe water film due to the non-uniform properties of the metal substrate.Such non-uniformity can result from the differences in chemicalcomposition of the metal, differences in metal microstructure, or due tothe differences in mechanical stress of the surface of a metal. Suchnon-uniformity can lead to the formation of electrode potentialdifference on the surface. It is believed that when the surface of metalis covered by the electrolyte, such as water formed by the condensationof moisture, the locations with a lower electrode potential turn into ananode while the locations with a higher electrode potential turn into acathode. These anodes and cathodes, covered with the electrolyte, canform many micro electrochemical corrosion cells across over the entiresurface of metal, which in turn can produce corrosion. A workablecorrosion cell is generally composed of three sub-processes—an anodicprocess, a cathodic process, and an electrolyte pathway to transferionic species. The anode process in the corrosion is the metal thatloses electrons to form its ionic species and thus can be dissolved intothe electrolyte as illustrated in the following manner:

2Fe−4e(electron)=2Fe²⁺(ionic species)   1

When the condition is neutral, the cathode process in the corrosion isthe reduction of oxygen which gains the electrons released from theanode in the following manner:

O₂+2H₂O+4e(electron)=4OH⁻  2

This oxygen, required by the cathode process, generally comes from theoxygen dissolved in the water. In the electrolyte, such as water, Fe²⁺released from the anode transports towards cathode, and at the sametime, OH⁻ produced on the cathode transports toward anode. Eventually,they neutralize each other to keep the electrolyte at a neutralcondition. For a workable micro corrosion cell, the anode and cathodeprocess have to occur at the same time. The corrosion stops whenevereither of them is eliminated. For the corrosion of coated systems, asimilar corrosion mechanism occurs, but with some special featuresdescribed below.

Due to the coverage of metal surface by coating, it takes a long timefor the water to permeate through the coating thickness to approach theinterface of coating/metal substrate. Corrosion occurs only when thewater approaches the metal surface, or more specifically, the interfaceof coating/metal substrate. However, if the coating has defects, such asmicro-cracks, corrosion can be initiated immediately inside thesedefects. As a result, the corrosion data obtained by a conventional ACimpedance evaluation method, dictated or distorted by the intrinsicdefects of the coating, may not represent the actual true performance ofthe coating. As noted by the cathode reaction (in Equation 2 above), thepH of the cathode area is increased significantly when corrosion occurs.For many coating formulations, such an increased pH promotesdelamination of coating film from the metal substrate, which is one ofthe primary coating failure modes.

Under working conditions, these micro-anodes and micro-cathodes arerandomly distributed across the entire surface of metal substrate andthey are not distinguishable. However, in the device and process ofpresent invention, the anode and cathode are separated so that theseanodic and cathodic processes can be controlled and acceleratedindividually.

The preferred embodiment of this invention provide for:

An AC impedance method suitable for sensitively detecting any changecaused by the corrosion of metal substrate under the coating film;

A cathode separated from an anode in the device and process allows oneto respectively separately control and accelerate the corrosion processoccurring on the cathode and anode;

Artificial defects are provided on the anode and cathode so that theeffect of the intrinsic defects can be eliminated.

The present invention provides for a device and a process forcomprehensively evaluating the performance of coatings under variouscontrolled and accelerated conditions. In the start up period, theperformance of the coatings is evaluated under a natural condition. Inthe stepped-up period, the performance of the coatings is evaluated atan accelerated condition. In this period, the anodic corrosion processat the anode site and the delamination process on the cathode site areaccelerated separately and gradually by means of sequentially stepped DCvoltages applied across the cathode and anode. The inhibitive effect atthe anode site, and the delamination resistance on the cathode site areevaluated at the same time. In the recovery period, the recoveryperformances of the coatings are evaluated after stopping the severecorrosion that occurs when stepped DC voltages are applied across thecathode and anode.

FIGS. 1 and 2 illustrate the typical anodic dissolution process thatoccurs at an anode (FIG. 1) and the delamination processes that occur ata cathode (FIG. 2) of the present invention.

FIG. 1 illustrates the anodic end of the device of the present inventionof a typical multi-coating system applied over a metal substrate 110,FIG. 1 includes a dry conversion coating layer (phosphate layer) 112typically ranging in thickness from 2 to 50 nanometers applied over ametal substrate 110, followed by a dry layer of an electro-coated primer114 typically ranging in thickness from 25 to 250 micrometers, thenfollowed by a dry layer of either a basecoating or a sealer-basecoatingcombination 116 typically ranging in thickness from 20 to 50 micrometersfor the sealer, and 50 micrometers to 120 micrometers for thebasecoating (color coating). Typically, basecoating 116 is protectedwith a dry layer of a clearcoating 118 ranging in thickness from 30micrometers to 100 micrometers. A standardized defect is represented bya defect 120 that exposes metal substrate 110 to an electrolyte 122,such as 3% sodium chloride containing dissolved oxygen. If the metalsubstrate 110 is a cold rolled steel, ferrous ions are released in theelectrolyte and over time, the surface of substrate 110 corrodes to formpits 124, rust scales etc. Then the size of defect 120 can increase overtime by corrosion, which then separates the multi-coating from metalsubstrate 110 and corrodes and damages the underlying surface.

FIG. 2 illustrates the cathodic end of the device of the presentinvention. FIG. 2 shows a typical multi-coating applied over anautomobile metal body 210, which includes a dry layer of a conversioncoating 212 applied over metal substrate 210, followed by a dry layer ofan electro-coated primer 214 followed by a dry layer of a basecoating216 followed by a dry layer of a clearcoating 218, all havingthicknesses mentioned in the paragraph above. A standardized defect isrepresented by a defect 220 that exposes metal substrate 210 to anelectrolyte 222, such as 3% sodium chloride containing dissolved oxygen.When cathodic reactions occur, driven by the DC voltages applied, it isbelieved the pH at the cathode site will be increased due to thereduction of oxygen, and a higher pH will promote the delamination ofthe multi-coating from metal substrate 210 thereby further exposing theunderlying metal surface. In addition, hydrogen 224 can be produced ifthe DC voltage applied is high enough, which can further promote adelamination process 226 (shown in FIG. 2) of the cathode by themechanical action from evolved hydrogen burbles.

Therefore, it is necessary to develop a testing device and processtherefor to expeditiously evaluate the corrosion resistance ofprotective coatings. One embodiment of a corrosion evaluator 1 for thepresent invention is shown in FIG. 3. Evaluator 1 includes a chamber 10,typically made of inert material, such as glass to retain an electrolyte12 therein. Chamber 10 is preferably cylindrical in shape. Some oftypical electrolytes can include an aqueous solution containing sodiumchloride at a concentration of 3 parts by weight based on 100 parts byweight of the aqueous solution, or an aqueous solution that simulatesacid rain or corrosive chemical solutions, such as those to whichtypical manufacturing equipment may be exposed. The aqueous solutioncontaining sodium chloride is preferably used.

One end of chamber 10 is provided with a flanged opening 14 over whichan anode holder 16 can be mounted to retain an anode 18 made fromvarious types of steel, aluminum, and copper. Anode 18 is coated with ananode coating 20 made of a single layer or a multilayer protectivecoatings resulting from an automotive OEM paint, automotive refinishpaint, marine paint, aircraft paint, architectural paint, industrialpaint, rubberized coating, polytetrafluoroethylene coating, or zinc-richprimer. One approach to prevent leaking of electrolyte 12 can be toprovide an ‘O’ ring 22 retained in a circular groove on the flange ofopening 14, whereby anode holder 16 retains anode 18 against ‘O’ ring22. Anode holder 16 can be made of flexible material, such as rubber orit could be a clamp that grips anode 18. Anode coating 20 is providedwith an anode defect 24 that exposes the surface of anode 18 toelectrolyte 12.

At the other end of chamber 10 is provided with a flanged opening 26over which a cathode holder 28 can be mounted to retain a cathode 30made from various types of steel, aluminum, and copper. Cathode 30 iscoated with a cathode coating 32 made of a single layer or a multilayerprotective coatings resulting from an automotive OEM paint, automotiverefinish paint, marine paint, aircraft paint, architectural paint,industrial paint, rubberized coating, polytetrafluoroethylene coating,or zinc-rich primer. One approach to prevent leaking of electrolyte 12can be to provided an ‘O’ ring 22 retained in a circular groove on theflange of opening 26, whereby cathode holder 28 retains cathode 30against ‘O’ ring 22. Cathode holder 28 can be made of flexible material,such as rubber or it could be a clamp that grips cathode 30. Cathodecoating 32 is provided with a cathode defect 36 that exposes the surfaceof cathode 30 to electrolyte 12.

Evaluator 1 further includes a conventional direct current variablepower generator 38 with DC output leads 41 that connect to anode 18 andcathode 30 such that desired DC voltages for desired durations can beapplied across anode 18, cathode 30, and electrolyte 12. Direct currentvariable power generator 38 is also in communication with a conventionalcomputer 40, such as the one supplied by Dell Computer Corporation ofRound Rock, Tex. Evaluator 1 is provided with a conventional directcurrent measurement device 42 for measuring DC voltage applied acrossanode 18, cathode 30, and electrolyte 12. Direct current measurementdevice 42 is also in communication with computer 40.

Evaluator 1 further includes a conventional alternating current variablepower generator 44 with AC output leads 46 that connect to anode 18 andcathode 30 for applying desired AC voltages at variable frequencies fordesired durations across anode 18, cathode 30, and electrolyte 12.Alternating current variable power generator 44 is also in communicationwith computer 40. Generally, AC voltage applied is about 10 to 50 mV(milliVolt), 20 to 30 mV is preferred.

Evaluator 1 further includes a conventional impedance measurement device46 with leads 48 that connect to anode 18 and cathode 30 for measuringimpedance across anode 18, cathode 30, and electrolyte 12. Impedancemeasurement device 46 is also in communication with computer 40. Thefollowing explanation provides for the basic concept utilized inimpedance measurements.

Impedance is a more general parameter that describes a circuit's abilityto resist the flow of electrical current. An electrical current can befully characterized by its amplitude and frequency characterized by acomplex function. Similarly, the impedance is usually also described asa complex function. The impedance is more general, since it also coversthe case of DC current by simply assuming the frequency (f) is zero.

The impedance (Z) of a circuit can be described by the combination ofthree ideal electrical elements, namely inductor (L), capacitor (C), andresistor (R) by the following equations:

Z(L)=j2πfL   (3)

Z(C)=−j1/(2πfC)   (4)

Z(R)=R   (5).

Where: f is the frequency in Hz

L is the quantity of the inductance

C is the quantity of the capacitance

J is a symbol of complex function; √−1

It can be shown that the impedance of a resistor is independent offrequency, while the impedance of an inductor is increased as a functionof frequency and the impedance of a capacitor is inversely proportionalto the frequency. As mentioned above, in most cases, the impedance (Z)of a circuit is usually the combination of three ideal electricalelements and the actual impedance can be described by the followingcomplex function:

Z(L, C, R)=Z(L)+Z(C)+Z(R)=R+j(2πfL−1/(2πfC))=real part+j imaginary part  (6)

Evaluator 1 further includes a computer usable storage medium 50 locatedin computer 40, which is in communication with direct current variablepower generator 38, direct current measurement device 42, alternatingcurrent variable power generator 44 and impedance measurement device 46,wherein computer readable program code means 400 (described in FIGS. 4A,4B, 4C and 4D) reside in said computer usable storage medium 50.

Computer readable program code means 400 include:

means 410 for configuring computer readable program code devices tocause computer 40 to subject said portions of anode coating 20 andcathode coating 32 to a start-up period, which can range from half anhour to one thousand hours, preferably from 3 to 15 hours.

means 412 for configuring computer readable program code devices tocause computer 40 to direct impedance measurement device 46 to measuren1 set of impedances A during the start-up period at preset intervals,wherein each said set of AC impedances A are measured at presetfrequencies ranging from 100000 to 10⁻⁶ Hz, preferably from 10000 to10⁻² Hz, of AC power supplied by alternating current variable powergenerator 44.

means 414 for configuring computer readable program code devices tocause computer 40 to determine start-up solution resistances(^(Sta)R_(Sol.n1)) by selecting a real part of said impedance A at astart-up solution frequency selected from 500 to 100000 Hz, preferablyfrom 5000 to 10000 Hz, from each said set of the impedances A.

means 416 for configuring computer readable program code devices tocause computer 40 to determine start-up resistances (^(Sta)R_(Sta.n1))by selecting a real part of impedance A at a start-up frequency selectedfrom 10⁻¹ to 10⁻⁶ Hz, preferably from 10⁻² to 10⁻³ Hz from each said setof the impedances A.

means 418 for configuring computer readable program code devices tocause computer 40 to direct current variable power generator 38 to applyn2 preset DC voltages in a stepwise manner for n2 preset durations,wherein direct current measurement device 42 in communication withcomputer 40 and connected to cathode 30 and anode 18 is used to measurethe preset DC voltages; and wherein the foregoing preset duration rangesfrom half an hour to ten hours, preferably from half an hour to twohours. Typically DC voltages range from half a volt to four volts withhalf a volt increments.

means 420 for configuring computer readable program code devices tocause computer 40 to direct impedance measurement device 46 to measure aset of impedances B at the end of each of the preset duration at thepreset frequencies of AC power with said amplitude supplied byalternating current variable power 44 generator to produce n2 said setsof said impedances B.

means 422 for configuring computer readable program code devices tocause computer 40 to determine stepped-up solution resistances(^(Stp)R_(sol.n2)) by selecting a real part of said impedance B atstepped-up solution frequency selected from 500 to 100000 Hz, preferablyfrom 5000 to 10000 Hz, from each said set of the impedances B.

means 424 for configuring computer readable program code devices tocause computer 40 to determine stepped-up resistances (^(Stp)R_(Stp.n2))by selecting a real part of impedance B at a stepped-up frequencyselected from 10⁻¹ to 10⁻⁶ Hz, preferably from 10⁻² to 10⁻³ Hz, fromeach said set of the impedances B.

means 426 for configuring computer readable program code devices tocause computer 40 to subject the portions of anode coating 20 andcathode coating 32 to n3 preset recovery periods in between each of saidpreset durations wherein said preset recovery periods range from half anhour to ten hours, preferably from 30 minutes to 3 hour.

means 428 for configuring computer readable program code devices tocause computer 40 to direct impedance measurement device 46 to measure aset of impedances C at the end of each of the preset recovery periods atthe preset frequencies of AC power with said amplitude supplied byalternating current variable power generator 44 to produce n3 said setsof said impedances C.

means 430 for configuring computer readable program code devices tocause computer 40 to determine recovery solution resistances(^(Rec)R_(sol.n3)) by selecting a real part of impedance C at a recoveryfrequency selected from 500 to 100000 Hz, preferably from 5000 to 10000Hz, from each said set of the impedances C.

means 432 for configuring computer readable program code devices tocause computer 40 to determine recovery resistances (^(Rec)R_(Rec.n3))by selecting a real part of impedance C at recovery frequency selectedfrom 10⁻¹ to 10⁻⁶ Hz (preferred (10⁻² to 10⁻³ Hz) from each said set ofsaid impedances C.

means 434 for configuring computer readable program code devices tocause computer 40 to calculate corrosion performance resistance(R_(perf)) of anode 18 and cathode 30 pair by using the followingequation:

R _(perf)=[Σ^(Sta) f _(n1)(^(Sta) R _(Sta.n1)−^(Sta) R_(Sol.n1))]/n1+[Σ^(Stp) f _(n2)(^(Stp) R _(Stp.n2)−^(Stp) R_(Sol.n2))]/n2+[Σ^(Rec) f _(n3)(^(Rec) R _(Rec.n3)−^(Rec) R_(Sol.n3))]/n3, wherein n1, n2, n3 and n3 range from 1 to 100,preferably n1 ranges from 5 to 15, n2 and n3 range from 3 to 10; and^(Sta) f _(n1), ^(Stp) f _(n2), and ^(Rec) f _(n3) range from 0.0000001to 1, preferably range from 0.1 to 1.

Generally, n2 is equal to n3. By way of clarification, if n1 is 5, theninside sigma, n1 in the numerator would be 1, 2, 3, 4, and 5 and n1 inthe denominator would be 5.

means for 436 configuring computer readable program code devices tocause computer 40 to direct a computer monitor 52 to display thecorrosion performance resistance (R_(perf)), direct a printer 54 toprint the corrosion performance resistance (R_(perf)), transfer thecorrosion performance resistance (R_(perf)) to a remote computer 56 or aremote database, or a combination thereof.

FIG. 5 illustrates one of the typical protocols used in the process ofthe present invention. Total time for performing the test can range from2 hours to 350 hours, preferably 20 hours to 40 hours.

Preferably, direct current variable power generator 38, direct currentmeasurement device 42, alternating current variable power generator 44and impedance measurement device 46 can all be positioned in a singlestand-alone unit for convenience and ease of operation. Such a unit(Unit B1) was obtained from Solartron Analytical located at Farnborough,Hampshire, United Kingdom.

In order to eliminate the effect of random intrinsic defects ofcoatings, applicants made a surprising discovery that by deliberatelycreating the standardized defects of known sizes and shapes on cathodeand anode coatings and exposing the underlying anode/cathode surface toan electrolyte, the anodic dissolution of the underlying anodes and thedelamination process of the underlying cathodes can be substantiallyaccelerated in a predictable and reproducible manner when DC voltage areapplied across the cathode and anode. FIG. 6 illustrates suchdeliberately created defects 618, 620, and 622 on anode or cathodecoating 612 applied over a cathode or anode 610 that is positionedagainst chamber 614 having an ‘O’ ring 616. The most desirable defect isdefect 620, although Defect 618 is acceptable since it does expose theunderlying surface of cathode or anode 610 to the electrolyte, whereasdefect 622 is unacceptable as it does not expose the underlying surfaceof cathode or anode 610 to the electrolyte.

Preferably, anode or cathode defect, as illustrated in FIG. 7 include aplurality of circular openings 712 disposed on coating 710 that exposethe underlying surface of the anode or cathode to the electrolyte.Circular openings 712 preferably have a diameter in the range of from 5micrometers to 3 millimeters, each circular opening 712 being uniformlyseparated from one another by 10 to 2000 times the diameter of circularopenings 712. As a result, corrosion effect illustrated by a zone 714 onone opening 712 does not spill over and affect the corrosion process onan adjacent opening 712A. Alternatively, anode or cathode coating 710can be provided with 1 to 100 of circular openings 712 per squarecentimeter of said cathode or anode.

Preferably, anode 18 and cathode 30 have identical shape (preferablycircular) and thickness. Preferably, anode coating 20 is identical tocathode coating 32 and preferably, anode defect 24 is identical tocathode defect 36. As a result, any deviations between the set ofcathode and anode can be eliminated.

Evaluator 1 can be provided with a thermal jacket 54 to maintain thetemperature of electrolyte 12 at a desired temperature. Typically, aheat transfer fluid 56, such as water can be used to maintain thetemperature of electrolyte 12 in the range of 0.5° C. to 99.5° C. Aconventional temperature probe 58 in communication with computer 40 canbe used to maintain the temperature of electrolyte 12 at a desiredtemperature.

Evaluator 1 can be configured to provide two or more chambers wherebyall such chambers can be maintained under similar conditions forcomparing the corrosion resistance of one set of protective coatingsagainst other, i.e., cathodes having different types of cathode coatingsapplied thereon can be compared for coating delamination performance(the lesser the delamination the better will be coating corrosionresistance properties). Similarly, anodes paired with correspondingcathodes having identical anode coatings applied thereon can be comparedfor corrosion resistance of one type of said anode coating to the othertype of said anode coating. Preferably, each paired cathode and anodewill have identical coating applied thereon. FIG. 8 illustratesmulti-chamber 800 construction whereby chambers 810 provided withthermometer wells 816 are enclosed within a thermal jacket 812 withoutlet 818.

FIG. 9 shows a cross-section of the embodiment of the present inventionof FIG. 8 taken along the cross-section 9-9. Embodiment 900 includesanode assembly 910 and cathode assembly 912 forming a leg 914 of aninverted ‘Y’ (λ) to permit any gas generated in electrolyte 916 duringuse or gas bubbles adhered on the surface of coated coupons duringinstallation to escape readily from a cylindrical chamber 918, which canbe provided with a thermal jacket 920 containing heat transfer fluid 922having an inlet 924 and an outlet 926. Chamber 918 can be furtherprovided with a thermometer well 928 and a support 930.

In the alternative, applicants also contemplate another embodiment ofthe present invention wherein a chamber in the form of inverted ‘U’ (∩)with the anode and cathode positioned at the bottom of each leg of theinverted ‘U’ shaped chamber having an opening at the apex of theinverted ‘U’ shaped chamber to permit any gas generated in theelectrolyte during use to escape readily from the chamber.

The present invention is also directed to a process that utilizes theevaluator 1 described in FIG. 3. The process evaluates the corrosionresistance of anode coating 20 applied over a surface of anode 18 andcorrosion resistance of cathode coating 32 applied over a surface ofcathode 30 by utilizing the following steps:

(i) sealably positioning anode 18 in anode holder 16 located on chamber10 of corrosion resistance evaluator 1, chamber 10 containingelectrolyte 12 therein such that a portion of anode coating 20 isexposed to electrolyte 12, the portion of anode coating 20 having anodedefect 24 thereon;

(ii) sealably positioning cathode 30 in cathode holder 28 located onchamber 10 such that a portion of cathode coating 32 is exposed toelectrolyte 12, the portion of cathode coating 32 having cathode defect36 thereon;

(iii) directing computer 40 of evaluator 1 through computer readableprogram code means 400 (shown in FIGS. 4A, 4B, 4C and 4D) residing onusable storage medium 50 located in computer 40 and configured to causecomputer 40 to perform following steps comprising:

-   -   (a) subjecting the portions of anode coating 20 and cathode        coating 30 to a start-up period;    -   (b) directing impedance measurement device 46 in communication        with computer 40 and is connected to cathode 30 and said anode        18 to measure n1 set of impedances A during the start-up period        at preset intervals, wherein each said set of impedances A are        measured at preset frequencies ranging from 100000 to 10⁻⁶ Hz of        AC power with an amplitude ranging from 10 to 50 mV at desired        AC voltages supplied by alternating current variable power        generator 44 in communication with computer 40, alternating        current variable power generator 44 having AC output leads 46        that connect to cathode 30 and anode 18;    -   (c) determining start-up solution resistances (^(Sta)R_(sol.n1))        by selecting a real part of the impedance A at a start-up        solution frequency selected from 500 to 100000 Hz from each said        set of the impedances A;    -   (d) determining start-up resistances (^(Sta)R_(Sta.n1)) by        selecting a real part of impedance A at a start-up frequency        selected from 10⁻¹ to 10⁻⁶ Hz from each said set of said        impedances A;    -   (e) directing direct current variable power generator 38 to        apply n2 preset DC voltages in a stepwise manner for n2 preset        durations, wherein direct current variable power generator 38 is        in communication with computer 40 and is connected to cathode 30        and anode 18; and wherein direct current measurement device 42        in communication with computer 40 and connected to cathode 30        and anode 18 is used to measure said preset DC voltages;    -   (f) directing impedance measurement device 46 to measure a set        of impedances B at the end of each of said preset duration at        said preset frequencies of AC power at said amplitude supplied        by alternating current variable power generator 44 to produce n2        said sets of said impedances B;    -   (g) determining stepped-up solution resistances        (^(Stp)R_(sol.n2)) by selecting a real part of said impedance B        at stepped-up solution frequency selected from 500 to 100000 Hz        from each said set of said impedances B;    -   (h) determining stepped-up resistances (^(Stp)R_(Stp.n2)) by        selecting a real part of impedance B at a stepped-up frequency        selected from 10⁻¹ to 10⁻⁶ Hz from each said set of said        impedances B;    -   (i) subjecting said portions of anode coating 20 and cathode        coating 32 to n3 preset recovery periods in between each of said        preset durations;    -   (j) directing impedance measurement device 46 to measure a set        of impedances C at the end of each of said preset recovery        periods at said preset frequencies of AC power at said amplitude        supplied by alternating current variable power generator 44 to        produce n3 said sets of said impedances C;    -   (k) determining recovery solution resistances (^(Rec)R_(sol.n3))        by selecting a real part of impedance C at a recovery frequency        selected from 500 to 100000 Hz from each said set of said        impedances C;    -   (l) determining recovery resistances (^(Rec)R_(Rec.n3)) by        selecting a real part of impedance C at recovery frequency        selected from 10⁻¹ to 10⁻⁶ Hz from each said set of said        impedances C;    -   (m) calculating corrosion performance resistance (R_(perf)) of        said anode and said cathode pair by using the following        equation:

R _(perf)=[Σ^(Sta) f _(n1)(^(Sta) R _(Sta.n1)−^(Sta) R_(Sol.n1))]/n1+[Σ^(Stp) f _(n2)(^(Stp) R _(Stp.n2)−^(Stp) R_(Sol.n2))]/n2+[Σ^(Rec) f _(n3)(^(Rec) R _(Rec.n3)−^(Rec) R_(Sol.n3))]/n3, wherein n1, n2, n3 and n3 range from 1 to 100; and^(Sta) f _(n1), ^(Stp) f _(n2), and ^(Rec)f_(n3) range from 0.0000001 to1; and

-   -   (n) causing computer 40 to direct a computer monitor 52 to:        -   (n1) display the corrosion performance resistance            (R_(perf)),        -   (n2) direct a printer 54 to print the corrosion performance            resistance (R_(perf)),        -   (n3) transfer the corrosion performance resistance            (R_(perf)) to a remote computer 56 or a remote database, or        -   (n4) a combination thereof.

The process of the present invention can be used comparing the corrosionresistance of one type of coating against another type of coating bytesting them under similar conditions and protocol by utilizing multiplechambers such as those shown in FIG. 8. Cathodes having different typesof cathode coatings applied thereon and said anodes having differenttypes of anode coatings applied thereon can be compared to evaluatedelamination resistance of one type of cathode coating to the other typeof cathode coating. It should be understood that each set of pairedcathode and anode would have identical coating applied thereon.Simultaneously, anodes having different types of anode coatings appliedthereon can be compared to evaluate corrosion resistance of one type ofanode coating to the other type of anode coating.

EXAMPLES Comparative Corrosion Data from Conventional Corrosion TestMethod

The correlation between a conventional 40-day cyclic corrosion test andthe corrosion test of the present invention was performed by using eightconventional E-coat systems. To vary the corrosion performance, eightE-coating systems designated as coating A, B, C, D, F, G, H and Icomprising different phosphate pretreatments, different formulations,different baking temperatures and baking times were applied on testpanels made of cold rolled steel. All the test panels were identical insize, shape and thickness. A coated test panel was defined as a coupon.After coating was applied and cured, each coupon was scribed with gridpattern. The conventional 40-day cyclic corrosion test used in thecorrelation verification utilized 40 cycles of the corrosion test. Eachcycle lasting 24 hours included the first 8 hour of electrolyte sprayexposure comprising repeated sequences consisting of half hour exposureto electrolyte spray followed by one and half hours of a rest period.The electrolyte used was a mixture of 0.9% NaCl, 0.1% CaCl₂ and 0.25%NaHCO₃, all in weight percentage based on the total weight. Theforegoing eight hour electrolyte spray exposure was followed by 8.0 hourhumidity exposure at 50° C. and 100% RH and then 8.0 hour exposure at60° C. in oven. Duplicate coupons for each of the E-coating systems wereused in the test. Each coupon after the aforedescribed conventionalcorrosion test was subjected to creep test using a conventional creepmeasurement device and the creep in millimeters was reported. The creepdata were then transferred into the corrosion resistance by using thefollowing equation:

Equivalent corrosion resistance (ohm)=B/Creep=300000/Creep

wherein B is a transformation factor in ohm/mm, which can be affected bythe kind of metal substrate used and the aggressiveness of the corrosiontesting method. The data transformation was necessary for the purpose ofcomparison since the data obtained by the corrosion resistance evaluatorof the present invention were in the form of corrosion resistance.

Corrosion Data from the Corrosion Test Method of the Present Invention

Eight E-coating systems designated as coating A, B, C, D, F, G, H and Iwere applied on coupons and cured. On the coated surfaces of suchcoupons, six holes with a diameter of 300 microns were drilled toprovide standardized anode and cathode defect, respectively. Each of theholes penetrated through the thickness of the coating and stopped at theinterface of metal/coating. Standardized anode and cathode defects wereidentical.

The corrosion test evaluator was based on a 26 hour test protocol thatincluded 5 sets of AC impedance measurements during 12 hours of start-upperiod (DC Volts=0), followed by four preset durations, each durationlasting two hours at stepped voltages starting from 0.5 Volts, followedby 1 Volt, 2 Volts, and 3 Volts. One set of AC impedance measurement wasperformed at the end of each preset duration. A 1.5 hour of recoveryperiod was used in between each preset duration. One set of AC impedancemeasurement was made at the end of each recovery period. The corrosionperformance resistance of the coating was calculated by using thefollowing equation:

R _(perf)=[Σ^(Sta) f _(n1)(^(Sta) R _(Sta.n1)−^(Sta) R_(Sol.n1))]/n1+[Σ^(Stp) f _(n2)(^(Stp) R _(Stp.n2)−^(Stp) R_(Sol.n2))]/n2+[Σ^(Rec) f _(n3)(^(Rec) R _(Rec.n3)−^(Rec) R_(Sol.n3))]/n3

wherein n1 is 5, n2 is 4, and n3 is 4 and ^(Sta)f_(n1), ^(Stp)f_(n2),and ^(Rec)f_(n3) are all equal to 1.

The foregoing ^(Sta)R_(Sta.n1), ^(Stp)R_(Stp.n2), and _(Rec)R_(Rec.n3)were determined by the real part of the ac impedance at 10⁻² Hz fromeach of the respective ac impedance measurements obtained in therespective periods. ^(Sta)R_(Sol.n1), ^(Stp)R_(Sol.n2), and^(Rec)R_(Sol.n3) were determined by the real part of the ac impedance at100000 Hz from each of the respective ac impedance measurements obtainedin the respective periods. The following provides further explanation ofvarious element used in measuring the foregoing elements:

A typical ac impedance data (for coating H) obtained by the method ofthis invention can be described in FIG. 10. The impedance data wasobtained using a frequency scan from 100000 Hz 10⁻² Hz. This plot iscalled Nyquist plot with a minus imaginary part as Y axis and a realpart as X axis. The shortcoming of this plot is that the frequency isnot explicitly expressed in the plot. Since the impedance, as notedearlier, is frequency dependent, the impedance is changed when thefrequency is changed. By the impedance data at various frequencies(normally from 100000 Hz to 10⁻² Hz), the resistance component andcapacitance component can be separated and obtained respectively. Forexample, on the far left hand of FIG. 10 which is expanded as FIG. 11, asolution resistance in the start up period, ^(Sta)R_(Sol.2), can beobtained by selecting the real part of the impedance at 100000 Hz. Onthe far right hand of FIG. 10, which is expanded as FIG. 12, a start upresistance ^(Sta)R_(Sta.2) can be obtained by selecting the real part ofthe impedance at 10⁻² Hz. The value of (^(Sta)R_(Sta.2)−^(Sta)R_(Sol.2))is also showed in FIG. 10, which can be used to calculate the corrosionresistance of the coating tested.

The corrosion resistance data obtained by the corrosion evaluator of thepresent invention and a conventional cyclic corrosion test is shown inFIG. 13. From FIG. 13, one can readily observe that there wassubstantial correlation between the convention carrion test method andthe corrosion test method of the present invention. The correlationcoefficient of these two methods can be calculated by using theconventional definition of Pearson product-moment correlationcoefficient. The Pearson product-moment correlation coefficient is awell-known correlation coefficient indicating the strength and directionof a linear relationship between two random variables. The correlationcoefficient of these two methods was 74%, which is very high compared tothe correlation coefficient between any other two conventional coatingevaluation methods, which is less than 55%. Therefore, the acceleratedcorrosion resistance evaluator correlates very well with theconventional corrosion test method.

The discrepancy observed in the coating evaluation tests is primarilydue to the difficulty in preparing the coated samples with the exactlysame quality and the subjective nature of the evaluation methods used inthe conventional corrosion tests.

The discrepancy observed on E-coating G can be explained in thefollowing manner:

For the same E coating formulation, the pretreatments should be rankedfrom the best to the poorest as Zn phosphate>iron phosphate>none. Thisranking is well known based on the prior experience and the knowledge ofcorrosion science. It was shown from FIG. 13 that both methods cancorrectly identify this ranking (compare coating A, B, and C in onegroup and compare coating F, G, and H in the second group). Also fromFIG. 13 and Table 1 below, it can be seen that most of the data showedthat for the same pretreatment, E-coating 2 performs better thanE-coating 1 (compare coating F to coating A, coating G to coating B,coating H to coating C, and coating I to coating D). The corrosionevaluation method of the present invention identified such a trend with100% accuracy while the conventional cyclic corrosion methods identifythis trend with only one exception of coating G. Therefore, it is highlylikely that the data of the coating G obtained by the method of thepresent invention is more accurate and more trustable.

TABLE 1 E-coated coupons for the correlation test Label PretreatmentE-coating Bake Time and Temperature A None E-coating 1 10 minutes at360° F. B Iron phosphate E-coating 1 10 minutes at 360° F. C Znphosphate E-coating 1 10 minutes at 360° F. D Zn phosphate E-coating 118 minutes at 310° F. E None E-coating 2 10 minutes at 360° F. G Ironphosphate E-coating 2 10 minutes at 360° F. H Zn phosphate E-coating 210 minutes at 360° F. I Zn phosphate E-coating 2 18 minutes at 310° F.

1. A process for evaluating corrosion resistance of an anode coatingapplied over a surface of an anode and corrosion resistance of a cathodecoating applied over a surface of a cathode comprising: (i) sealablypositioning said anode in an anode holder located on a chamber of acorrosion resistance evaluator, said chamber containing an electrolytetherein such that a portion of said anode coating is exposed to saidelectrolyte, said portion of said anode coating having an anode defectthereon; (ii) sealably positioning said cathode in a cathode holderlocated on said chamber such that a portion of said cathode coating isexposed to said electrolyte, said portion of said cathode coating havinga cathode defect thereon; (iii) directing a computer of said evaluatorthrough computer readable program code means residing on a usablestorage medium located in said computer and configured to cause saidcomputer to perform following steps comprising: a) subjecting saidportions of said anode coating and said cathode coating to a start-upperiod; b) directing an impedance measurement device in communicationwith said computer and is connected to said cathode and said anode tomeasure n1 set of impedances A during said start-up period at presetintervals, wherein each said set of ac impedances A are measured atpreset frequencies ranging from 100000 to 10⁻⁶ Hz of AC power at desiredAC voltages with an amplitude ranging from 10 to 50 mV supplied by analternating current variable power generator in communication with saidcomputer, said alternating current variable power generator having ACoutput leads that connect to said cathode and anode; c) determiningstart-up solution resistances (^(Sta)R_(sol.n1)) by selecting a realpart of said impedance A at a start-up solution frequency selected from500 to 100000 Hz from each said set of said impedances A; d) determiningstart-up resistances (^(Sta)R_(Sta.n1)) by selecting a real part ofimpedance A at a start-up frequency selected from 10⁻¹ to 10⁻⁶ Hz fromeach said set of said impedances A; e) directing a direct currentvariable power generator to apply n2 preset DC voltages in a stepwisemanner for n2 preset durations, wherein said direct current variablepower generator is in communication with said computer and is connectedto said cathode and said anode; and wherein said direct currentmeasurement device in communication with said computer and connected tosaid cathode and said anode is used to measure said preset DC voltages;f) directing said impedance measurement device to measure a set ofimpedances B at the end of each of said preset duration at said presetfrequencies of AC power with said amplitude supplied by said alternatingcurrent variable power generator to produce n2 said sets of saidimpedances B; g) determining stepped-up solution resistances(^(Stp)R_(sol.n2)) by selecting a real part of said impedance B atstepped-up solution frequency selected from 500 to 100000 Hz from eachsaid set of said impedances B; h) determining stepped-up resistances(^(Stp)R_(Stp.n2)) by selecting a real part of impedance B at astepped-up frequency selected from 10⁻¹ to 10⁻⁶ Hz from each said set ofsaid impedances B; i) subjecting said portions of said anode coating andsaid cathode coating to n3 preset recovery periods in between each ofsaid preset durations; j) directing said impedance measurement device tomeasure a set of impedances C at the end of each of said preset recoveryperiods at said preset frequencies of AC power with said amplitudesupplied by said alternating current variable power generator to producen3 said sets of said impedances C; k) determining recovery solutionresistances (^(Rec)R_(sol.n3)) by selecting a real part of impedance Cat a recovery frequency selected from 500 to 100000 Hz from each saidset of said impedances C; l) determining recovery resistances(^(Rec)R_(Rec.n3)) by selecting a real part of impedance C at recoveryfrequency selected from 10⁻¹ to 10⁻⁶ Hz from each said set of saidimpedances C; m) calculating corrosion performance resistance (R_(perf))of said anode and said cathode pair by using the following equation:R _(per)=[Σ^(Sta) f _(n1)(^(Sta) R _(Sta.n1)−^(Sta) R_(Sol.n1))]/n1+[Σ^(Stp) f _(n2)(^(Stp) R _(Stp.n2)−^(Stp) R_(Stp.n2))]/n2+[Σ^(Rec) f _(n3)(^(Rec) R _(Rec.n3)−^(Rec) R_(Sol.n3))]/n3, wherein n1, n2, n3 and n3 range from 1 to 100; and^(Sta) f _(n1), ^(Stp) f _(n2), and ^(Rec) f _(n3) range from 0.0000001to 1; and n) causing computer 40 to direct a computer monitor 52 to:(n1) display the corrosion performance resistance (R_(perf)), (n2)direct a printer 54 to print the corrosion performance resistance(R_(perf)), (n3) transfer the corrosion performance resistance(R_(perf)) to a remote computer 56 or a remote database, or (n4) acombination thereof.
 2. The process of claim 1 wherein said cathode andsaid anode are made of steel.
 3. The process of claim 1 wherein saidanode coating and said cathode coating results from a multilayer coatingcomposition comprising an automotive OEM paint, an automotive refinishpaint, a marine paint, an aircraft paint, an architectural paint, anindustrial paint, a rubberized coating, a polytetrafluoroethylenecoating, or a zinc-rich primer.
 4. The process of claim 1 wherein saidchamber is surrounded by a thermal jacket to maintain temperature ofsaid electrolyte at a desired temperature ranging from 0.5° C. to 99.5°C.
 5. The process of claim 1 wherein two or more of said chambers aresurrounded by a thermal jacket to maintain temperature of saidelectrolyte in each of said chambers at a desired temperature rangingfrom 0.5° C. to 99.5° C.
 6. The process of claim 1 wherein said anodecoating is identical to said cathode coating.
 7. The process of claim 1or 6 wherein said anode defect is identical to said cathode defect. 8.The process of claim 1 or 6 wherein said anode defect comprises aplurality of circular openings disposed on said coating that expose saidunderlying surface of said anode to said electrolyte.
 9. The process ofclaim 1 or 6 wherein said cathode defect comprises a plurality ofcircular openings disposed on said coating that expose said underlyingsurface of said cathode to said electrolyte.
 10. The process of claim 9wherein said cathode or anode defect comprises circular openings eachhaving a diameter in the range of from 5 micrometers to 3 millimeters,each said circular opening being uniformly separated from one another by10 to 1000 times the diameter of said circular openings.
 11. The processof claim 10 wherein said cathode or anode defect comprises in the rangeof from 1 to 100 of said circular openings per square centimeter of saidcathode or anode, said circular opening being uniformly separated fromone another, and wherein said circular opening has a diameter in therange of from 5 micrometers to 3 millimeters.
 12. The process of claim 1wherein said electrolyte comprises: (a) an aqueous solution containingsodium chloride at a concentration of 3 parts by weight based on 100parts by weight of said aqueous solution, (b) an aqueous solution thatsimulates acid rain, or (c) a corrosive chemical solution.
 13. Theprocess of claim 1 wherein said anode holder and said cathode holdereach form a leg of an inverted ‘Y’ to permit any gas generated duringuse to escape readily from said chamber.
 14. The process of claim 1wherein said anode holder and said cathode holder are positioned at theopposite ends of said chamber to permit any gas generated during use toescape readily from said chamber.
 15. The process of claim 1 whereinsaid start-up period ranges from half an hour to one thousand hours. 16.The process of claim 1 wherein said preset interval ranges from half anhour to ten hours.
 17. The process of claim 5 wherein said cathodes havedifferent types of cathode coatings applied thereon and said anodes havedifferent types of anode coatings applied thereon for comparingdelamination of one type of said cathode coating to the other type ofsaid cathode coating, and to compare corrosion resistance of one type ofsaid anode coating to the other type of said anode coating.
 18. Theprocess of claim 17 wherein in each said chamber said cathode coatingand said anode coating is the same.
 19. The process of claim 18 whereinthickness of said cathode coating and said anode coating in each of saidchambers is the same.